Multiband Hybrid Metasurfaces

• Multiband hybrid metasurfaces are compact engineered structures that integrate distinct resonant subsystems, such as metal-dielectric, dielectric, or stacked designs, to achieve multifunctional electromagnetic responses.
• They leverage mechanisms like coupled gap-surface and localized surface plasmon modes, spectral filtering with phase control, and impedance-sheet synthesis to realize multiple resonant bands.
• Practical implementations demonstrate applications in optical communications, nonlinear spectroscopy, and imaging, while challenges include strict fabrication tolerances and efficiency trade-offs.

Searching arXiv for papers on multiband hybrid metasurfaces and related dual-/multi-band metasurface design. {"query":"multiband hybrid metasurface second-harmonic generation gap surface plasmon metasurface arXiv", "max_results": 5} {"query":"(Xiong et al., 2023) OR (Mondal et al., 5 Mar 2026) OR (Budhu et al., 2021)", "max_results": 10} A multiband hybrid metasurface is a metasurface architecture in which multiband or multifunctional electromagnetic response is obtained by combining distinct resonant subsystems, materials, or layers within a single compact structure. In the cited literature, this designation covers at least three concrete realizations: a metal-dielectric-metal bar-disc resonator supporting multiple gap-surface plasmon and localized surface plasmon modes with enhanced second-harmonic generation (Mondal et al., 5 Mar 2026); an all-dielectric VIS-NIR device that reflects 940 nm light into a specified direction while transmitting visible light from 450 nm to 750 nm by combining an aperiodic distributed Bragg reflector with dielectric meta-tokens (Xiong et al., 2023); and dual band stacked metasurfaces synthesized through an integral-equation framework in which multiple patterned metallic claddings are homogenized as coupled impedance sheets (Budhu et al., 2021). Taken together, these works show that “hybrid” is an architectural descriptor rather than the name of a single canonical platform.

1. Architectural forms

The metal-dielectric-metal multiband hybrid metasurface reported in 2026 adopts an aluminum bottom layer, a silicon dioxide spacer, and a bar-disc hybrid resonator patterned in the top aluminum layer. The bottom Al mirror has thickness $h_3 = 150\,\mathrm{nm}$, the SiO$_2$ spacer has thickness $h_2 = 70\,\mathrm{nm}$ with $n \approx 1.45$, and the top patterned Al layer has thickness $h_1 = 30\,\mathrm{nm}$. Its unit cell is periodic in both transverse directions with $P_x=P_y=900\,\mathrm{nm}$ and contains a bar of width $a_1=180\,\mathrm{nm}$ and length $a_2=485\,\mathrm{nm}$, a disc of radius $r_1 \approx 150\,\mathrm{nm}$, and a bar-disc edge-to-edge gap $d_1=50\,\mathrm{nm}$ (Mondal et al., 5 Mar 2026).

The all-dielectric VIS-NIR dual-function metasurface uses a fused-silica substrate with an aperiodic DBR made of 21 alternating layers of Si$_2$0N$_2$1 and SiO$_2$2, topped by TiO$_2$3 nanopillars. The bottom 19 layers form a standard quarter-wave stack for $_2$4, while the top two layers are detuned to provide extra phase control. At $_2$5, the reported refractive indices are $_2$6, $_2$7, and $_2$8 (Xiong et al., 2023).

The dual band stacked metasurface design of Budhu, Michielssen, and Grbic is conductor-backed and consists of two metasurfaces, each described as a patterned metallic cladding supported by a dielectric spacer, stacked one upon the other. The formulation is explicitly one-dimensionally invariant, and its synthesis proceeds from homogenized sheet impedances rather than from direct unit-cell parameter sweeps (Budhu et al., 2021).

Realization	Hybrid composition	Demonstrated role
(Mondal et al., 5 Mar 2026)	Al/SiO$_2$9/Al bar-disc metal-dielectric-metal cavity	Four-band resonant response and numerically investigated SHG
(Xiong et al., 2023)	Aperiodic Si$h_2 = 70\,\mathrm{nm}$0N$h_2 = 70\,\mathrm{nm}$1/SiO$h_2 = 70\,\mathrm{nm}$2 DBR plus TiO$h_2 = 70\,\mathrm{nm}$3 meta-tokens	NIR anomalous reflection with visible transmission
(Budhu et al., 2021)	Two stacked patterned metallic claddings homogenized as impedance sheets	Dual-band reflective beam formation

This diversity of implementations indicates that multiband hybrid metasurfaces need not be restricted to a single material system. In one case, hybridization is between GSP and LSP physics within a plasmonic cavity; in another, between a spectral filter and a phase-engineering layer; in another, between stacked reactive sheets coupled through dielectric regions.

2. Resonant physics and governing equations

In the plasmonic multiband device, the constituent resonances are separated into localized surface plasmon dipole modes, described as edge-charge oscillations on the bar or disc and weakly dependent on the spacer, and gap-surface plasmon cavity modes, described as standing waves in the SiO$h_2 = 70\,\mathrm{nm}$4 gap under each resonator. Four distinct reflection minima occur at $h_2 = 70\,\mathrm{nm}$5, $h_2 = 70\,\mathrm{nm}$6, $h_2 = 70\,\mathrm{nm}$7, and $h_2 = 70\,\mathrm{nm}$8. Their reported modal assignments are: $h_2 = 70\,\mathrm{nm}$9 at $n \approx 1.45$0 as bar-dominated LSP, $n \approx 1.45$1 at $n \approx 1.45$2 as a hybrid LSP-GSP mode, $n \approx 1.45$3 at $n \approx 1.45$4 as the first-order GSP under the bar, and $n \approx 1.45$5 at $n \approx 1.45$6 as the first-order GSP under the disc (Mondal et al., 5 Mar 2026).

The corresponding lateral cavity condition is stated as

$n \approx 1.45$7

where $n \approx 1.45$8 is the in-plane propagation constant of the GSP, $n \approx 1.45$9 is the effective lateral cavity length, $h_1 = 30\,\mathrm{nm}$0 is the reflection phase at resonator edges, and $h_1 = 30\,\mathrm{nm}$1 is the integer mode order. The approximate planar metal-insulator-metal dispersion is given by

$h_1 = 30\,\mathrm{nm}$2

with

$h_1 = 30\,\mathrm{nm}$3

and, in the limit of thick metals,

$h_1 = 30\,\mathrm{nm}$4

The vertical spacer field profile is

$h_1 = 30\,\mathrm{nm}$5

In the dielectric VIS-NIR device, spectral selectivity originates in the DBR and phase control in the TiO$h_1 = 30\,\mathrm{nm}$6 meta-token layer. For $h_1 = 30\,\mathrm{nm}$7 effective high/low index pairs, the stopband reflectance is written as

$h_1 = 30\,\mathrm{nm}$8

which yields $h_1 = 30\,\mathrm{nm}$9 reflectivity at $P_x=P_y=900\,\mathrm{nm}$0 and $P_x=P_y=900\,\mathrm{nm}$1 reflectivity across $P_x=P_y=900\,\mathrm{nm}$2–$P_x=P_y=900\,\mathrm{nm}$3. A single TiO$P_x=P_y=900\,\mathrm{nm}$4 nanopillar on the DBR has reflection coefficient

$P_x=P_y=900\,\mathrm{nm}$5

and parameter sweeps show that for $P_x=P_y=900\,\mathrm{nm}$6, $P_x=P_y=900\,\mathrm{nm}$7 can be swept over $P_x=P_y=900\,\mathrm{nm}$8 by varying the radius from $P_x=P_y=900\,\mathrm{nm}$9 with $a_1=180\,\mathrm{nm}$0 at $a_1=180\,\mathrm{nm}$1. Anomalous reflection is governed by the reported generalized Snell law

$a_1=180\,\mathrm{nm}$2

The unit-cell dimensions are $a_1=180\,\mathrm{nm}$3 and $a_1=180\,\mathrm{nm}$4, with the latter chosen to be below $a_1=180\,\mathrm{nm}$5 to suppress visible diffraction (Xiong et al., 2023).

In the stacked dual-band design, the central physical object is the spatially varying impedance sheet $a_1=180\,\mathrm{nm}$6 replacing each patterned cladding. The boundary condition is written as

$a_1=180\,\mathrm{nm}$7

and the resulting EFIE is discretized by the method of moments into the matrix system

$a_1=180\,\mathrm{nm}$8

The formalism is explicitly used to model mutual coupling both within each metasurface and from metasurface to metasurface, rather than treating the layers as independent (Budhu et al., 2021).

3. Synthesis strategies

The dielectric VIS-NIR device is synthesized by combining quarter-wave DBR design, RCWA optimization of the detuned top layers, and geometric phase selection of TiO$a_1=180\,\mathrm{nm}$9 nanopillars. For the standard DBR pairs, the thicknesses are reported as

$a_2=485\,\mathrm{nm}$0

The aperiodic top two layers are optimized to approximately $a_2=485\,\mathrm{nm}$1 for the first Si$a_2=485\,\mathrm{nm}$2N$a_2=485\,\mathrm{nm}$3 layer and $a_2=485\,\mathrm{nm}$4 for the second SiO$a_2=485\,\mathrm{nm}$5 layer. The three-pillar group in each cell realizes a $a_2=485\,\mathrm{nm}$6 linear phase ramp using radii $a_2=485\,\mathrm{nm}$7, heights of $a_2=485\,\mathrm{nm}$8, and center-to-center spacings $a_2=485\,\mathrm{nm}$9 (Xiong et al., 2023).

The plasmonic multiband design is tuned by systematic sweeps of the geometrical parameters. When the bar width $r_1 \approx 150\,\mathrm{nm}$0 is swept from $r_1 \approx 150\,\mathrm{nm}$1, $r_1 \approx 150\,\mathrm{nm}$2 red-shift by approximately $r_1 \approx 150\,\mathrm{nm}$3 while $r_1 \approx 150\,\mathrm{nm}$4 is nearly fixed. When the bar length $r_1 \approx 150\,\mathrm{nm}$5 is swept from $r_1 \approx 150\,\mathrm{nm}$6, similar red-shifts of approximately $r_1 \approx 150\,\mathrm{nm}$7 are obtained for the GSP-related modes, with the LSP-bar mode nearly unchanged. Sweeping the disc radius $r_1 \approx 150\,\mathrm{nm}$8 from $r_1 \approx 150\,\mathrm{nm}$9 red-shifts $d_1=50\,\mathrm{nm}$0 and $d_1=50\,\mathrm{nm}$1 by approximately $d_1=50\,\mathrm{nm}$2, while sweeping the spacer thickness $d_1=50\,\mathrm{nm}$3 from $d_1=50\,\mathrm{nm}$4 produces a pronounced red-shift of the GSP modes with $d_1=50\,\mathrm{nm}$5, leaving the LSP modes unaffected (Mondal et al., 5 Mar 2026).

The stacked dual-band synthesis is organized into three explicit phases. In Phase 1, patterned metallic claddings are homogenized and the nonlinear EFIE plus MoM solution yields complex-valued sheet impedances at both bands. In Phase 2, optimization transforms those complex-valued impedances into purely reactive sheets by enforcing

$d_1=50\,\mathrm{nm}$6

and minimizing the root-mean-square far-field error

$d_1=50\,\mathrm{nm}$7

In Phase 3, the reactive sheet impedances are translated into PCB patterns using a pre-tabulated library of five element topologies: gap capacitors, interdigitated capacitors, parallel-LC shunts, straight inductors, and meanders (Budhu et al., 2021).

These three synthesis routes are methodologically distinct. One is resonance mapping in a metal-insulator-metal cavity, one is spectral filtering plus phase programming in an all-dielectric structure, and one is inverse synthesis through coupled integral equations. This suggests that multiband hybrid metasurface design is not reducible to a single “unit-cell tuning” paradigm.

4. Experimental realizations and performance metrics

For the plasmonic multiband device, the optimized-geometry resonance metrics are reported as follows: $d_1=50\,\mathrm{nm}$8 with $d_1=50\,\mathrm{nm}$9 and $_2$00 together with near-unity absorptance $_2$01; $_2$02 with $_2$03, $_2$04, and $_2$05; $_2$06 with $_2$07, $_2$08, and $_2$09; and $_2$10 with $_2$11, $_2$12, and $_2$13. The fabricated array has a footprint of $_2$14. Reflectance measurements using a broadband halogen source, polarizer, $_2$15 optics with $_2$16, and OSA yielded x-polarized peaks at $_2$17, $_2$18, $_2$19, and $_2$20, and y-polarized peaks at $_2$21 and $_2$22. The reported simulation-experiment offset is $_2$23–$_2$24 and is attributed to fabrication tolerances and surface roughness (Mondal et al., 5 Mar 2026).

For the VIS-NIR dual-function metasurface, RCWA predicts a first-order NIR diffraction efficiency for TE polarization at $_2$25 with a peak of approximately $_2$26 at $_2$27 incidence and an average of approximately $_2$28 over $_2$29 incidence, corresponding to a $_2$30 full field of view. Visible zero-order transmission at normal incidence is approximately $_2$31 on average from $_2$32 to $_2$33, and the visible angular bandwidth is approximately $_2$34 for zero order exceeding $_2$35. Experimentally, the measured first-order NIR diffraction efficiency rises from approximately $_2$36 at $_2$37 to approximately $_2$38 at $_2$39, stays approximately $_2$40 to $_2$41, and then slowly drops, with an average over the full field of view of approximately $_2$42. Measured visible transmission averages approximately $_2$43, peaks at approximately $_2$44 near $_2$45, and is approximately $_2$46 at $_2$47 and $_2$48. The approximately $_2$49 loss relative to simulation is attributed to absorption and roughness in ALD TiO$_2$50 and non-Gaussian beam coupling (Xiong et al., 2023).

For the dual-band stacked designs, representative results include a Wi-Fi design with broadside far-field scans at $_2$51 and $_2$52 and reflection coefficient $_2$53 at both bands, as well as a second example with a lower-band scan to $_2$54 at $_2$55 and upper-band broadside response at $_2$56. In the latter case, the reported nonlinear iterative design converges in fewer than 10 iterations, and in both examples the MoM and COMSOL patterns are described as having excellent overlap or tracking closely (Budhu et al., 2021).

A consistent pattern across these demonstrations is that multiband performance is obtained together with clear fabrication sensitivity. In the dielectric device, pillar radius errors of $_2$57 correspond to phase errors of $_2$58 and an efficiency drop of approximately $_2$59–$_2$60, while height uniformity of $_2$61 and DBR top-layer thickness control within $_2$62 are identified as important for phase matching (Xiong et al., 2023).

5. Nonlinear conversion and multifunctionality

In the multiband plasmonic metasurface, second-harmonic generation is analyzed numerically rather than experimentally. The retained nonlinear source term is the surface-normal component

$_2$63

with the SHG intensity scaling as

$_2$64

The far-field SH response is expressed through the Lorentz-reciprocity overlap integral

$_2$65

For a peak pump intensity of $_2$66 with $_2$67 pulses at $_2$68, the simulated SHG conversion efficiencies are approximately $_2$69 at $_2$70 ($_2$71), approximately $_2$72 at $_2$73 ($_2$74), approximately $_2$75 at $_2$76 ($_2$77), and approximately $_2$78 at $_2$79 ($_2$80), with field-enhancement factors of approximately $_2$81, $_2$82, $_2$83, and $_2$84, respectively (Mondal et al., 5 Mar 2026).

The dielectric VIS-NIR metasurface demonstrates a different form of multifunctionality. At $_2$85 the nanopillars support high-$_2$86 resonances that produce nearly unity reflection amplitude and a geometry-tunable phase, while in the visible range from $_2$87 to $_2$88 Mie-type modes are leaky, yielding greater than $_2$89 zero-order transmission with essentially flat phase, so the metasurface is transparent. The same device therefore functions as an NIR steering element and a visible window (Xiong et al., 2023).

The stacked impedance-sheet formalism further broadens the meaning of multifunctionality by targeting different far-field patterns at different frequencies. The reported two-band examples generate collimated beams at desired angles in each band upon reflection, and the optimization toward purely reactive sheets introduces evanescent lobes in the plane-wave spectra that are indicative of surface-wave power redistribution (Budhu et al., 2021).

These examples distinguish at least three operational senses of “multifunctional”: spectral partitioning between transmission and reflection, coexistence of multiple resonant absorption bands with nonlinear frequency conversion, and frequency-dependent beam synthesis in a stacked reflector.

6. Applications, limitations, and open directions

The reported applications of the all-dielectric VIS-NIR device include compact imaging optics and metalenses for augmented-reality eye-tracking, multispectral sensors combining visible transmission for color imaging with NIR beam steering for depth sensing or LiDAR, and free-space beam steering or optical communications requiring both visible transparency and NIR redirection in a single ultrathin element (Xiong et al., 2023). The plasmonic multiband device is positioned for telecommunications across the O, S, and C bands, nonlinear spectroscopy through on-chip SHG sources at multiple wavelengths, and integrated nanophotonics including beam steering, filtering, and frequency conversion (Mondal et al., 5 Mar 2026).

The limitations are also explicit. In the plasmonic case, experimental SHG was left for future studies, so the nonlinear performance remains numerically investigated rather than experimentally validated (Mondal et al., 5 Mar 2026). In the dielectric case, rainbow artifacts at visible band edges lower throughput, and measured efficiency degradation is linked to ALD TiO$_2$90 absorption, roughness, non-Gaussian beam coupling, and nanofabrication tolerances (Xiong et al., 2023). In the integral-equation framework, extension beyond two bands increases the number of field-matching conditions, makes the sub-wavelength condition stricter at the highest frequency, enlarges the block MoM systems at each frequency, and demands richer element libraries and more advanced global optimizers. The cited text also notes that ensuring local power conservation simultaneously at multiple frequencies may require injecting multiple surface-wave channels or higher-order evanescent spectra (Budhu et al., 2021).

A terminological ambiguity follows from these studies. “Hybrid” may refer to hybrid LSP-GSP modal character, to a hybrid spectral-phase stack such as DBR plus meta-tokens, or to a stacked-sheet synthesis in which multiple patterned layers are coupled through the field solution. This suggests that the technically important question is not whether a metasurface is hybrid in name, but which degrees of freedom are hybridized: material composition, cavity type, resonant mechanism, or inverse-design formulation.

Across the cited works, multiband hybrid metasurfaces are therefore characterized by controlled coexistence of distinct resonances or functionalities within a compact platform, but the enabling mechanism varies substantially. In plasmonic metal-dielectric-metal implementations, the decisive ingredient is coupled GSP-LSP modal engineering; in all-dielectric VIS-NIR platforms, it is the combination of spectral selectivity and phase-programmable reflection; in stacked reflective systems, it is coupled impedance-sheet synthesis under EFIE and MoM constraints.